Control system for laundry dryers



Oct. 23, 1962 G. D. CONLEE 3,059,344

CONTROL SYSTEM FOR LAUNDRY DRYERS Filed May 2a, 1958 AUTOMATIC M AN UAL COOL AND STOP AlR TUMBLE HEAT OFF DRY DAMP DRY HEAVY DUTY HEAT ON 42% r 1 a4 5a 3o 35 WM... Geofle Dilonlee a? @1 fi g m4 v% nit I) George D. Coulee, Ripon, Wis, assignor to McGraw- Edison Company, Ripon, Wis, a corporation of Dela- Ware Filed May 26, 1958, Ser. No. 737,704 3 Claims. (Cl. 34-45) The invention relates to laundry dryers and more particularly, to an improved control system for such dryers.

One object of the invention is to provide a control system by which the operation of a dryer may be varied to obtain precisely the right drying conditions for a wide variety of fabrics.

Another object is to provide a control system which is selectively settable to operate the dryer in any one of a plurality of different types of cycles, each of which is especially well adapted for a specific drying job.

A more specific object is to provide a control system which is selectively settable to operate in either an automatic or manually controlled cycle and with or without heating of the circulating air as required for the particular fabrics being dried.

A further object is to provide improved means for introducing a timed cooling operation at the end of each operating cycle in which the circulating air is heated.

Other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment illustrated in the accompanying drawings in which FIGURE 1 is a face view of a control panel for use with the improved control system.

FIG. 2 is a circuit diagram of the improved control system.

FIG. 3 is a diagrammatic view showing the driving arrangement for the drum and fan of the dryer.

While a single preferred embodiment of the invention has been shown and will be described herein in detail, it is not intended that the detailed character of the disclosure should limit the invention to such particulars but the intention is to cover all modifications and adaptations falling within the spirit and scope of the invention as more broadly and generally characterized in the appended claims.

For purposes of illustration, the invention has been shown as incorporated in a dryer control system of the general type disclosed and claimed in my copending application with Leo V. Buck, Serial No. 647,056 filed March 19, 1957. Control systems of this character are especially well suited for use with domestic laundry dryers of the type in which the load of clothes or other fabrics to be dried is tumbled in a drum 5 (FIG. 3) supported for rotation about a horizontal axis. The drum is rotatably driven by a motor M whichalso drives a fan or blower 6 for directing a stream of air through the drum. For heating the circulating air, the exemplary dryer is provided with an electrically operated heater H which, in this instance, comprises two resistance type heating elements 7 and 8.

A control system of the type selected to illustrate the invention provides for automatically terminating a drying cycle when the material in the drum reaches a predetermined state of dryness. The control system constituting the present invention provides precisely the same type of automatic cycling and additionally is adapted to be preset to provide other types of drying cycles. Moreover, by reason of the novel circuit arrangement, the setting of the controls for a desired type of cycling may be effected by simply turning a control knob 9 to a selected one of a plurality of positions.

The knob 9 constitutes the actuating member of a multi-position selector switch MS. The particular switch shown is a four-position rotary switch equipped with two movable switch arms 19 and 11. It is conveniently mounted in the housing of the dryer, preferably in a compartment defined by an upwardly formed portion 12 of the top Wall of the housing extending along the back edge of the top. The knob 9 is presented at the front of a panel 13 provided with suitable indicia for identifying the type of operation afforded in each position of the switch MS.

The exemplary control system is constructed and arranged to provide three dififerent types of cycling, which have been found to meet practically all conditions encountered in home laundries. Thus, one setting of the selector switch provides a fully automatic cycle such as that referred to above. The position of the switch MS for such a cycle is designated by the legend Automatic on the panel 13 adjacent an index mark 18 against which an indicator 19 on the knob may be set. The automatic cycle normally provides for a complete drying of the load of fabrics undergoing treatment but it may be modified to bring the cycle to an end when the load is damp dry. Such modification is conveniently effected by an auxiliary two-position switch 20 (FIG. 2) operable by a knob 21 at the front of the panel 13. The two switch, positions may be identified respectfully by the legends Dry and Damp Dry as shown in FIG. 1.

Another drying cycle involving the tumbling of the load of fabrics in a stream of unheated air is designated by the legend Air Tumble-Heat Off on the panel. The switch position for this operation is identified by an index mark 22 positioned for registry with the indicator 19 of the knob 9.

A third drying cycle involving the tumbling of the load of fabrics for an indeterminate period with maximum heat input to the circulating air is conveniently designated on the panel by the legend Heavy Duty-I-Ieat On. An index mark 23 positioned for cooperation with the indicator 19 indicates the position of the selector switch.

In addition to the foregoing cyclic operations, the controls may be set by appropriate manipulation of the knob 9 to interrupt any of the operating cycles. Cycles involving the heating of the circulating air are followed by a cooling period in which air circulation is continued for a predetermined period without the application of heat. The position of the switch MS for terminating cycles is designated on the panel 13 by the legend ManualCool and Stop and an index mark 24.

Having in mind the various types of drying cycles obtainable with the improved control system, the preferred construction and circuitry of the system can be most readily described with reference to its mode of operation. Thus, to operate the dryer in a conventional automatic cycle, the knob 9 is turned to set the indicator 19 at the index mark 18. The switch arm 11 is thereby moved into engagement with a switch contact 25 while switch arm 10 is moved to an open circuit position. For complete drying, the knob 21 is set in Dry position, thus closing switch 20 as shown in FIG. 2.

A drying cycle is initiated by momentary actuation of a push buton S mounted, in this instance, on the portion 12 of the dryer housing adjacent the panel 13. The push button is arranged to actuate a series of switches associated with and operable by a control relay CR. One switch 30 is closed to complete an energizing circuit for the control relay CR by way of a conductor 31, normally closed contacts 32 of a temperature responsive device TR, closed switch contacts 20, conductor 33, selector switch contact 25 and arm 11, conductor 34 to one terminal of the relay. The other terminal of the relay is connected by a conductor 35 with vthe neutral conductor N of a three-wire line by which electric current is supplied to the dryer. Switch 30 is connected receives sulficient heat fromthe heater through a door operated switch 36 and conductor 3'1 to' conductor L1 of the power line. The relay CR when energized, holds the push-button operated switches in the position to which they. were actuated by the push button and the relay is thus locked up under control of auxiliary devices including the temperature responsive device TR. The temperature responsive device TR and a timing device TD cooperate to measure the evaporative rate obtaining in the dryer and act to deenergize the control relay and terminate the cycle when the load in the dryer is completely dry. The temperature responsive device TR, which may be of any preferred construction, is positioned so as to sense the temperature of the exhaust air, that is, the air leaving the dryer after passing through or over the material being dried. It includes the switch contacts 32 and a second set of contacts 38, both of which are normally closed and which are opened when 'the'exhaust air temperature rises to a predetermined value.

While a spring or motor driven timing device may be used if desired, the exemplary control system employs a heat actuated device as the timer TD. This device is positioned to respond 'to the heat generated by the heating coil 8 of the heater H. It includes a thermostatic element 40 controlling switch contacts 41,- the arrangement being such that when the element 40 becomes heated, the contacts 41 are closed. Upon deenergization of the heating element 8, the thermostatic element 40 cools downand, after a measured time interval, opens the switch :c'ont-acts 41. This time interval is used for measuring the evaporative rate or, in other words, 'to define the interval during which the amount of sensible heat converted to latent heat of evaporation is measured. Other circuits closed by the push button S and maintained closed by the relay CR include a starting and running circuit 'for the motor M. This circuit extends prom-line conductor L1 by way of conductor 37, switch contacts 42, conductor 43 to a centrifugal switch 44 proy-ided in the motor; With the motor stopped or running below normal operating speed, switch 44 connects the starting and running windings of the motor to conductor 53, the other terminals of those windings being connected to the neutral conductor of the power line by way ofa conductor 45; When the motor reaches normal operating-speeds, switch 44 disconnects the starting winding, leaving the running winding in circuit to continue the operation of the motor.

I Closure of the switch 42 together with closure of a switch 46 of control relay CR completes circuits for heating elements '7 and 8, As will be seen by reference to FIG. 2, one terminal of each heating element is connected to conductor 43 which is connected to line conductor Ll upon closure of switch 42. Closure of switch? completes the circuit from line conductor L2, conductors 47 and 48 to the other terminals of heating element 7. A branch conductor 49 from the conductor 18 extends by way of timer switch contacts 38 to the other terminal of heating element 8. Q

The motor M and heater H having been placed in operation, the drying cycle proceeds with the drum rotating to tumble the load being dried while the tan 5 circulates "air we; the heater and through the drum. Shortly after this operation starts, timing device TD 7 to close switch contacts41 and establish a shunt circuit around contacts 32 for purposes to appear presently. Also positioned to receiveheat-from the heater is a massive e'lement 50 of heat retaining metal or othertsuitable materialadjacent which is mounted a thermostatic "element 51. The elemerit '51 when heated closes'switch contacts 5 to pre pare an auxiliary circuit for the motor M to be described later on. a I V .When thefload in the drum reaches what may be called a damp-dry condition, the ternperaturebf the exhaust airrises rapidly and at a predetermined temperature thermostatic device TR opens switches 32 and-.38.

The opening of the latter switch interrupts the circuit for heating element 8 so that the circulating air receives heat only from the element 7. With the decreased heat input, the exhaust air temperature will drop. The emperature drop will be relatively rapid if there is still a substantial amount of moistuie in the load due to the continued evaporation and the conversion of sensible heat to latent heat of vaporization. On the other hand, if the load is substantially dry, the temperature drop will be slower by reason of the decreased evaporative rate.

The operations of the temperature responsive device TR and the timing device TD are coordinated so that the operating cycle is terminated when the load reaches a desired degree of dryness. More particularly, when the initial operation of the device TR takes place while there is still a substantial amount of moisture in the load, the exhaust temperature will drop sufiiciently fast to bring about a closure of the switches 32 and 38 before the end of the time interval measured by the timer TD and marked by the opening of the switch contacts 41. Closure of the switch 32 under those conditions reestablishes the holding circuit for control relay CR and closure of switch 38 completes the energizing circuit 'for the heating element 8. Accordingly, the drying operation with full application of heat is resumed and continues until the temperature responsive device is again actuated by the exhaust temperature rising to the predetermined level.

The above sequence of operations will be repeated until the load reaches the desired degree of dryness. When that condition is reached, the slower cooling rate, measured by the temperature of the exhaust air, prevents reclosure of contacts 32 and 38 within the time interval measured by the timing device TD. Opening of the timing contacts 43; before reclosure of contacts 32 interrupts the holding circuit for control relay CR which becomes deenergized and thus terminates the operating cycle of the dryer.

In accordance with the invention, each operating cycle involving the heating of the circulating air is followed by a cooling period of predetermined length during which 'air is circulated through the drum 5 with the heater H shut off. This cooling period is controlled and timed by the temperature responsive device 51 which maintains its switch 52 closed until the heat stored in the mass 50 has been dissipated. The mass-5t of course, is proportioned to provide the desired interval which may be of any reasonable-length.

Switch 52 when closed in cooperation with switch con- 'tacts 53 closed upon deenergization of control relay CR complete a running circuit for the motor M independently of the switch 42 which maintains the motor operation during the initial portion of the cycle. Accordingly, motor M continues to run and drive the fan 6 and drum 5 'until the switch 52 opens at the end of the predetermined cooling interval.

Certain lightweight, delicate fabrics, as well assome of the synthetic fiber fabrics, are susceptible to heat damage and are therefore desirably dried without the application of heat. The improved-controls may be preset to provide suitable drying conditions for such fabrics by merely turning the knob 9 to set the indicator 19 in registry with the index 'mark 22. This brings th'eswitch arm 10 into engagement with a contact 54 and moves the switch arm '11 into open-circuit'position. Actuation of the push button S to start a cycle with the selector switch so positioned closesthe'relay switch contacts in the usual manner and, through switch contacts 42 a'nd 44, starts the motor M. -As soon as the motor M comes up to speed, the push button isreleased. The relay switch contacts return to their normal positions immediately as relay CR is not energized due to its open circuit at the' switch arm 11. The heater H is, momentarily energized through switches 42 and 46 butthat circuit is opened uponrelease or the push button and the heater remains inoperative through the cycle.

Closure of switch 53 upon release of the push button S establishes a new running circuit for the motor M by way of contact 54, switch arm 10 and centrifugal switch 44. Motor M continues to run and drive the fan 6 to circulate unheated air through the drum which is rotated in the usual way to tumble the load. The cycle proceeds for an indeterminate period, that is, until it is stopped by manual intervention. For this purpose, the selector switch is turned to set the indicator 19 at index mark 24. Switch arm 16 is thus moved to open position interrupting the motor circuit and terminating the drying cycle. As no heat is used in this type of operation, switch 52 remains open and consequently the dryer stops at once.

In contrast with the above, certain hard-to-dry fabrics such as cotton rugs and comparable heavy fabrics, require application of maximum heat for extended periods for satisfactory drying. The improved controls provide the proper drying conditions for such fabrics when preset by turning the selector switch to register the indicator 19 with the index mark 23. This positions the switch arms 18 and 11 as shown in FIG. 2, switch arm being in open circuit position and switch arm 11 engaged with a contact 55.

With the selector switch set as above, actuation of the push button S completes an energizing circuit for relay CR by way of switch contacts 30, contact 55 and switch arm 11. Relay CR when energized maintains switch 350 closed upon release of the push button and accordingly maintains a holding circuit for itself which is independent of the contacts 32 and 41 of the temperature responsive and timing devices TR and TD. Contacts 42 and 46 are also held closed by the control relay to energize the heater H and to keep the motor M running. Under those conditions, thermostatic device TR in responding to the temperature of the exhaust air, merely opens the circuit of the heating element 8 to prevent temperatures from becoming excessive. Heating element 7 operates continuously.

The above described cycle, conveniently called the Heavy Duty cycle, is indeterminate in length, that is, it continues until interrupted manually. To stop the cycle, the selector switch is turned to register the indicator 19 with the index mark 24. Switch arms 10 and 11 are both shifted to open circuit position, interrupting the heater circuit and releasing control relay CR. Motor M, however, continues in operation for the predetermined cooling period under control of the thermostatic device 51 and its switch 52 as before described.

It will be apparent from the foregoing that the invention provides a control system of novel and advantageous character for laundry dryers. By the simple positioning of a selector switch prior to starting the dryer, the controls may be conditioned to provide precisely the right drying conditions for a wide variety of fabrics. Thus, the controls may be quickly and easily preset to operate the dryer in either a fully automatic cycle or a manually controlled cycle with or without heating of the circulating air. The invention also provides novel means for introducing a timed cooling interval following either an automatic or manual cycle in which heating of the circulating air is involved.

I claim as my invention:

1. In a laundry dryer having a rotatable receptacle for material to be dried, a fan for circulating air through the receptacle, an electrical heating element for heating the circulating air, and a motor for driving the fan and rotating the receptacle, the control system comprising in combination,

a. a relay having a plurality of normally open switches and a normally closed switch,

b. manual start means for operating said sets of relay switches,

c. a circuit for said heating element including one of said normally open relay switches and a thermostatically controlled heat cycling relay for deenergizing and energizing said heating element at a predetermined high and a predetermined lower temperature of exhaust air from said receptacle,

d. means for sensing the dryness of material in said receptacle including a thermostatically controlled sensing switch adapted to open upon deenergization of said heating element and to close at said lower exhaust air temperature and a timed switch in parallel circuit therewith adapted to open a predetermined time after said sensing switch opens,

e. a start and running circuit for said motor including said one normally open relay switch,

1. a second running circuit for said motor including said normally closed relay switch in series with a centrifugally controlled switch closed at running speeds of said motor and a thermostatically controlled cool-down switch open at low temperatures,

g. a circuit for energizing said relay including a second one of said normally open relay switches, and

h. a multiposition selector switch having (1) a [first position for completing said relay circuit through said parallel circuit sensing means for automatically opening said relay circuit when the exhaust air temperature fails to reach said lower temperature within said predetermined time and for continuing operation of said motor until said cool-down switch opens,

(2) a second position for completing said relay circuit and by-passing said sensing means for continuous operation of said motor and heating element between said high and lower temperatures,

(3) a third position for opening said relay circuit and for by-passing said cool-down switch for continued operation of said motor through said second running circuit after actuation of said start means, and

(4) a fourth position for manually and selectively opening said relay circuit and continuing operation of said motor through said second running circuit until said cool-down switch opens.

2. The combination as claimed in claim 1 in which a manually operated switch is connected in series with said timed switch for selectively disabling the latter to cause said relay to be deenergized when said sensing switch opens initially and said multiposition switch is in its first position for damp drying of said material.

3. In a laundry dryer having a rotatable receptacle for material to be dried, a fan for circulating air through the receptacle, an electrical heating element for heating the circulating air, and a motor for driving the fan and rotating the receptacle, the control system comprising in combination, I

a. a relay having a plurality of normally open switches and a normally closed switch,

b. manual start means for operating said sets of relay switches,

c. a circuit for said heating element including one of said normally open relay switches and a thermostatically controlled heat cycling relay for deenergizing and energizing said heating element at a predetermined high and a predetermined lower temperature of exhaust air from said receptacle,

d. switch means adapted to open when material in said receptacle reaches a predetermined condition of dryness,

e. a start and running circuit for said motor including said one normally open relay switch,

1. a second running circuit for said motor including said normally closed relay switch in series with a centrifugally controlled switch closed at running speeds of said motor and a thermostatically controlled cool-down switch open at low temperatures,

a h. a multiposition selector switch having (1) a first position for completing said relay circuit through said switch means for automatically opening said relay circuit when said switch means opens and for continuing operation of said motor until said cool-down switch opens,

(2) a second position for completing said relay circuit and bypassing said sensing means for continuous operation of said motor and heating element between said high and lower temperatures,

(3) a third position for opening said relay circuit and for by-passing said cool-down switch for continued operation of said motor through said second running circuit after actuation of said start means, and

(4) a fourth position for manually and selectively opening said relay circuit and continuing operation of said motor through said second running circuit until said cool-down switch opens.

References Cited in the file of this patent UNITED STATES PATENTS Dunkelman Sept. 16, 1958 

